The present invention relates generally to a demixing (separation) of multiple acoustic source signals from mixtures of these signals. More particularly, the present invention relates to estimating delay and attenuation compensation parameters for Blind Source Separation (BSS) and to providing channel selection for the separated source signals.
As known to those skilled in the art, hearing devices assist people with hearing problems. A hearing device may be a hearing aid, a middle-ear implant, a cochlear-implant, or a brainstem implant, and normally includes a microphone to pick up acoustical signals, a signal processor to process the signals, and an output device. The output device may be a receiver for a hearing aid, a mechanical vibrator for a middle-ear implant, or an electrode array for cochlear implants.
In noisy environments, a typical omnidirectional microphone picks up the desired signals and the interfering noise at the same time. Depending on the signal-to-noise ratio, the signals may be masked by the noise and are hard to detect for the user of the hearing device. Several processing methods were suggested to distinguish between signals and the background noise by assuming a difference between both inputs. An assumption is, for example, that there is different frequency content (spectrum) between the signal and the noise exist and a different time structure. These processing methods, however, cannot distinguish between the desired signals and the background signals if they both contain speech, because then the frequency and time structure are similar.
One processing method that may be used in the above situations is blind source separation (BSS). Namely, BSS is a signal separation technique capable of improvements in signal to noise ratio for mixtures of independent signals, such as multiple voices or voice plus noise signals. The principles of operation of BSS are fundamentally different to those of other noise reduction approaches, such as the spectral subtraction mentioned above.
One problem, however, still hinders the devices with the conventional BSS method: it cannot be predicted on which channel each separated source will appear. The conventional BSS method uses only statistical independence between sources, and statistical independence contains no information about the scale or the order of the sources. Estimates of the sources can be recovered up to an arbitrary scale and arbitrary permutation. This effectively means that a BSS algorithm operating on blocks of data may separate sources in some order at one time, and in a different order the next time. The uncertainty about which signal is separated on a channel renders the conventional algorithm practically unusable. This problem is known in the art as the channel selection problem. To solve the channel selection problem, some other information is required to break the permutation symmetry between outputs.
A need therefore exists for a system and method that addresses the above concerns and overcomes the disadvantages of conventional BSS techniques used in hearing devices, for example.
It is an object of the present invention to provide a fast blind source separation technique.
It is another object of the present invention to provide a solution to the channel selection problem.
It is yet another object of the present invention to separate two voices for voice mixtures even when the sources have very similar spectral power characteristics.
The above and other objects are achieved by a digital signal processing device for carrying out a blind source separation. A mixture of at least two source signals is inputted to the digital signal processing device. A number of fractionally delayed measurements of the mixture is performed, and differences between the fractionally delayed measurements are cross-correlated. The cross-correlated results are minimized to obtain demixed sources.
In accordance with one aspect of the present invention, the digital signal processing device is located in a hearing device selected from a hearing aid, a middle-ear implant, a cochlear implant, and a brainstem implant.
In accordance with another aspect of the present invention, the blind source separation is performed in time domain or frequency domain.